Control of steam generation for chemical mechanical polishing

ABSTRACT

A chemical mechanical polishing system includes a steam generator with a heating element to apply heat to a vessel to generate steam, an opening to deliver steam onto a polishing pad, a first valve in a fluid line between the opening and the vessel, a sensor to monitor a steam parameter, and a control system. The control system causes the valve to open and close in accordance with a steam delivery schedule in a recipe, receive a measured value for the steam parameter from the sensor, receive a target value for the steam parameter, and perform a proportional integral derivative control algorithm with the target value and measured value as inputs so as to control the first valve and/or a second pressure release valve and/or the heating element such that the measured value reaches the target value substantially just before the valve is opened according to the steam delivery schedule.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/360,907, filed Jun. 28, 2021, which claims priority to U.S.Provisional Application No. 63/045,682, filed on Jun. 29, 2020, thedisclosures of which are incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to control of generation of steam forsubstrate processing tools, e.g., for chemical mechanical polishing(CMP).

BACKGROUND

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive, or insulativelayers on a semiconductor wafer. A variety of fabrication processesrequire planarization of a layer on the substrate. For example, onefabrication step involves depositing a filler layer over a non-planarsurface and polishing the filler layer until the top surface of apatterned layer is exposed. As another example, a layer can be depositedover a patterned conductive layer and planarized to enable subsequentphotolithographic steps.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier head. The exposed surface of thesubstrate is typically placed against a rotating polishing pad. Thecarrier head provides a controllable load on the substrate to push itagainst the polishing pad. A polishing slurry with abrasive particles istypically supplied to the surface of the polishing pad.

The polishing rate in the polishing process can be sensitive totemperature. Various techniques to control temperature during polishinghave been proposed.

SUMMARY

A chemical mechanical polishing system includes a platen to support apolishing pad, a carrier head to hold a substrate in contact with thepolishing pad, a motor to generate relative motion between the platenand the carrier head, a steam generator including a vessel having awater inlet and a steam outlet and a heating element configured to applyheat to a portion of lower chamber to generate steam, an arm extendingover the platen having at least one opening oriented to deliver steamfrom the steam generator onto the polishing pad, a first valve in afluid line between the opening and the steam outlet to controllablyconnect and disconnect the opening and the steam outlet, a sensor tomonitor a steam parameter, and a control system coupled to the sensor,the valve and optionally to the heating element. The control system isconfigured to cause the valve to open and close in accordance with asteam delivery schedule in a polishing process recipe stored as data ina non-transitory storage device, receive a measured value for the steamparameter from the sensor, receive a target value for the steamparameter, and perform a proportional integral derivative controlalgorithm with the target value and measured value as inputs so as tocontrol the first valve and/or a second pressure release valve and/orthe heating element such that the measured value reaches the targetvalue substantially just before the valve is opened according to thesteam delivery schedule.

Possible advantages may include, but are not limited to, one or more ofthe following.

Steam, i.e., gaseous H₂O generated by boiling, can be generated insufficient quantity to permit steam heating of the polishing pad beforepolishing of each substrate, and the steam can be generated at aconsistent pressure from wafer-to-wafer. Polishing pad temperature, andthus polishing process temperature, can be controlled and be moreuniform on a wafer-to-wafer basis, reducing wafer-to-wafernon-uniformity (WIWNU). Generation of excess steam can be minimized,improving energy efficiency. The steam can be substantially pure gas,e.g., have little to no suspended liquid in the steam. Such steam, alsoknown as dry steam, can provide a gaseous form of H₂O that has a higherenergy transfer and lower liquid content than other steam alternativessuch as flash steam.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other aspects,features, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional view of an example of a polishingstation of the polishing apparatus.

FIG. 1B is a schematic top view of an example polishing station of thechemical mechanical polishing apparatus.

FIG. 2 illustrates a control system that includes a proportionalintegral derivative control algorithm that can be performed to controlpower to a steam generator.

FIG. 3A is a schematic cross-sectional view of an example steamgenerator.

FIG. 3B is a schematic cross-sectional top view of an example steamgenerator.

DETAILED DESCRIPTION

Chemical mechanical polishing operates by a combination of mechanicalabrasion and chemical etching at the interface between the substrate,polishing liquid, and polishing pad. During the polishing process, asignificant amount of heat is generated due to friction between thesurface of the substrate and the polishing pad. In addition, someprocesses also include an in-situ pad conditioning step in which aconditioning disk, e.g., a disk coated with abrasive diamond particles,is pressed against the rotating polishing pad to condition and texturethe polishing pad surface. The abrasion of the conditioning process canalso generate heat. For example, in a typical one minute copper CMPprocess with a nominal downforce pressure of 2 psi and removal rate of8000 Å/min, the surface temperature of a polyurethane polishing pad canrise by about 30° C.

On the other hand, if the polishing pad has been heated by previouspolishing operations, when a new substrate is initially lowered intocontact with the polishing pad, it is at a lower temperature, and thuscan act as a heat sink. Similarly, slurry dispensed onto the polishingpad can act as a heat sink. Overall, these effects result in variationof the temperature of the polishing pad spatially and over time.

Both the chemical-related variables in a CMP process, e.g., as theinitiation and rates of the participating reactions, and themechanical-related variables, e.g., the surface friction coefficient andviscoelasticity of the polishing pad, are strongly temperaturedependent. Consequently, variation in the surface temperature of thepolishing pad can result in changes in removal rate, polishinguniformity, erosion, dishing, and residue. By more tightly controllingthe temperature of the surface of the polishing pad during polishing,variation in temperature can be reduced, and polishing performance,e.g., as measured by within-wafer non-uniformity or wafer-to-wafernon-uniformity, can be improved.

One technique that has been proposed to control the temperature of thechemical mechanical polishing process is to spray steam onto thepolishing pad. Steam might be superior to hot water because less steammay be required to impart an equivalent amount of energy as hot water,e.g., due to the latent heat of the steam.

In a typical polishing process, steam is applied in a duty cycle(typically measured as a percentage of the total time from start ofpolishing of one wafer to start of polishing of a subsequent wafer) thatcan range from 1% to 100%. If the duty cycle is lower than 100%, thesteam generation cycle can be split into two sections: a recuperationphase and a dispense phase.

Typically in the recuperation phase the vessel for steam generation isconsidered closed, i.e., the valve(s) are closed, so that steam cannotescape the vessel. Power is applied to a heater, e.g., a resistiveheater, to input heat energy to the liquid water in the vessel. Inaddition, liquid water may flow into the vessel to replace water lost ina previous dispense cycle.

In the dispense phase, the valves are opened so that the steam isdispensed. The steam generator might not be able to keep up with theflow rate of steam during the dispense phase, in which case the dispensephase is accompanied by a pressure drop in the vessel. In somesituations, when the heated liquid water exposed to atmosphere, therecan be an abrupt a phase change to gas, commonly referred to as flashsteam.

In general, during the recuperation phase, the goal is to add sufficientthermal energy to get steam ready for the next dispense phase, asdictated by parameters (temperature, flow rate, pressure) that may berequired for the process. In some cases, e.g., a 20 sec dispense phasefollowed by an 80 sec recuperation phase, the required steam pressurecan be achieved well before the beginning of the next dispense cycle. Inthis scenario, the power to the heater can turned off so as to avoidbringing the steam above the required parameters, e.g. pressure.However, the vessel is not a perfect insulator, so some heat loss canoccur, and the steam may not stay at the desired parameters.Alternatively, power to the heater can be maintained, and excess steamcan relieved, e.g., vented, to keep the required parameters, e.g.pressure. However, this consumes excess energy and is not energyefficient.

To address this issue, during a recuperation phase a control system cancontrol power applied to the heater, e.g., using a proportional integralderivative control algorithm, in such a way that the required parametersare achieved just before the beginning of the next dispense phase.

FIGS. 1A and 1B illustrate an example of a polishing station 20 of achemical mechanical polishing system. The polishing station 20 includesa rotatable disk-shaped platen 24 on which a polishing pad 30 issituated. The platen 24 is operable to rotate (see arrow A in FIG. 1B)about an axis 25. For example, a motor 22 can turn a drive shaft 28 torotate the platen 24. The polishing pad 30 can be a two-layer polishingpad with an outer polishing layer 34 and a softer backing layer 32.

The polishing station 20 can include a supply port, e.g., at the end ofa slurry supply arm 39, to dispense a polishing liquid 38, such as anabrasive slurry, onto the polishing pad 30. The polishing station 20 canalso include a pad conditioner with a conditioner disk to maintain thesurface roughness of the polishing pad 30.

A carrier head 70 is operable to hold a substrate 10 against thepolishing pad 30. The carrier head 70 is suspended from a supportstructure 72, e.g., a carousel or a track, and is connected by a driveshaft 74 to a carrier head rotation motor 76 so that the carrier headcan rotate about an axis 71. Optionally, the carrier head 70 canoscillate laterally, e.g., on sliders on the carousel, by movement alongthe track, or by rotational oscillation of the carousel itself.

The carrier head 70 can include a flexible membrane 80 having asubstrate mounting surface to contact the back side of the substrate 10,and a plurality of pressurizable chambers 82 to apply differentpressures to different zones, e.g., different radial zones, on thesubstrate 10. The carrier head 70 can include a retaining ring 84 tohold the substrate. In some implementations, the retaining ring 84 mayinclude a lower plastic portion 86 that contacts the polishing pad, andan upper portion 88 of a harder material, e.g., a metal.

In operation, the platen is rotated about its central axis 25, and thecarrier head is rotated about its central axis 71 (see arrow B in FIG.1B) and translated laterally (see arrow C in FIG. 1B) across the topsurface of the polishing pad 30.

In some implementations, the polishing station 20 includes a temperaturesensor 64 to monitor a temperature in the polishing station or acomponent of/in the polishing station, e.g., the temperature of thepolishing pad 30 and/or slurry 38 on the polishing pad. For example, thetemperature sensor 64 could be an infrared (IR) sensor, e.g., an IRcamera, positioned above the polishing pad 30 and configured to measurethe temperature of the polishing pad 30 and/or slurry 38 on thepolishing pad. In particular, the temperature sensor 64 can beconfigured to measure the temperature at multiple points along theradius of the polishing pad 30 in order to generate a radial temperatureprofile. For example, the IR camera can have a field of view that spansthe radius of the polishing pad 30.

In some implementations, the temperature sensor is a contact sensorrather than a non-contact sensor. For example, the temperature sensor 64can be thermocouple or IR thermometer positioned on or in the platen 24.In addition, the temperature sensor 64 can be in direct contact with thepolishing pad.

In some implementations, multiple temperature sensors could be spaced atdifferent radial positions across the polishing pad 30 in order toprovide the temperature at multiple points along the radius of thepolishing pad 30. This technique could be use in the alternative or inaddition to an IR camera.

Although illustrated in FIG. 1A as positioned to monitor the temperatureof the polishing pad 30 and/or slurry 38 on the pad 30, the temperaturesensor 64 could be positioned inside the carrier head 70 to measure thetemperature of the substrate 10. The temperature sensor 64 can be indirect contact (i.e., a contacting sensor) with the semiconductor waferof the substrate 10. In some implementations, multiple temperaturesensors are included in the polishing station 22, e.g., to measuretemperatures of different components of/in the polishing station.

The polishing system 20 also includes a temperature control system 100to control the temperature of the polishing pad 30 and/or slurry 38 onthe polishing pad. The temperature control system 100 includes a heatingsystem 104 that operates by delivering a temperature-controlled mediumonto the polishing surface 36 of the polishing pad 30 (or onto apolishing liquid that is already present on the polishing pad). Inparticular, the medium includes steam, e.g., from the steam generator410 (see FIG. 2A). The steam can be mixed with another gas, e.g., air,or a liquid, e.g., heated water, or the medium can be substantially puresteam. In some implementations, the additives or chemicals are added tothe steam.

The medium can be delivered by flowing through apertures, e.g., holes orslots, e.g., provided by one or more nozzles, on a heating delivery arm.The apertures can be provided by a manifold that is connected to asource of the heating medium.

An example heating system 104 includes an arm 140 that extends over theplaten 24 and polishing pad 30 from an edge of the polishing pad to orat least near (e.g., within 5% of the total radius of the polishing pad)the center of polishing pad 30. The arm 140 can be supported by a base142, and the base 142 can be supported on the same frame 40 as theplaten 24. The base 142 can include one or more an actuators, e.g., alinear actuator to raise or lower the arm 140, and/or a rotationalactuator to swing the arm 140 laterally over the platen 24. The arm 140is positioned to avoid colliding with other hardware components such asthe polishing head 70, pad conditioning disk 92, and the slurrydispensing arm 39.

Multiple openings 144 are formed in the bottom surface of the arm 140.Each opening 144 is configured to direct a gas or vapor, e.g., steam,onto the polishing pad 30. The arm 140 can be supported by a base 142 sothat the openings 144 are separated from the polishing pad 30 by a gap126. The gap 126 can be 0.5 to 5 mm. In particular, the gap 126 can beselected such that the heat of the heating fluid does not significantlydissipate before the fluid reaches the polishing pad. For example, thegap can be selected such that steam emitted from the openings does notcondense before reaching the polishing pad.

The heating system 104 can include a source of steam, e.g., a steamgenerator 410. The steam generator 410 are be connected to openings 144in the arm 140 by a fluid delivery line 146, which can be provide bypiping, flexible tubing, passages through solid body that provides thearm 140, or a combination thereof.

The steam generator includes 410 a vessel 420 to hold water, and aheater 430 to deliver heat to water in the vessel 420. Power can bedelivered to the heater 430 from a power supply 250. A sensor 260 can belocated in the vessel 420 or in the fluid delivery line 146 to measure aphysical parameter, e.g., temperature or pressure, of the steam.

In some implementations, a process parameter, e.g., flow rate, pressure,temperature, and/or mixing ratio of liquid to gas, can be independentlycontrolled for each nozzle. For example, the fluid for each opening 144can flow through an independently controllable heater to independentlycontrol the temperature of the heating fluid, e.g., the temperature ofthe steam.

The various openings 144 can direct steam 148 onto different radialzones 124 on the polishing pad 30. Adjacent radial zones can overlap.Optionally, some of the openings 144 can be oriented so that a centralaxis of the spray from that opening is at an oblique angle relative tothe polishing surface 36. Steam can be directed from one or more of theopenings 144 to have a horizontal component in a direction opposite tothe direction of motion of polishing pad 30 in the region of impingementas caused by rotation of the platen 24.

Although FIG. 1B illustrates the openings 144 as spaced at evenintervals, this is not required. The nozzles 120 could be distributednon-uniformly either radially, or angularly, or both. For example,openings 144 could be clustered more densely toward the center of thepolishing pad 30. As another example, openings 144 could be clusteredmore densely at a radius corresponding to a radius at which thepolishing liquid 39 is delivered to the polishing pad 30 by the slurrydelivery arm 39. In addition, although FIG. 1B illustrates nineopenings, there could be a larger or smaller number of openings.

The temperature of the steam 148 can be 90 to 200° C. when the steam isgenerated (e.g., in the steam generator 410 in FIG. 2A). The temperatureof the steam can be between 90 to 150° C. when the steam is dispensed bythe nozzles 144, e.g., due to heat loss in transit. In someimplementations, steam is delivered by the nozzles 144 at a temperatureof 70-100° C., e.g., 80-90° C. In some implementations, the steamdelivered by the nozzles is superheated, i.e., is at a temperature abovethe boiling point (for its pressure).

The flow rate of the steam can be 1-1000 cc/minute when the steam isdelivered by the nozzles 144, depending on heater power and pressure. Insome implementations, the steam is mixed with other gases, e.g., ismixed with normal atmosphere or with Na. Alternatively, the fluiddelivered by the nozzles 120 is substantially purely water. In someimplementations, the steam 148 delivered by the nozzles 120 is mixedwith liquid water, e.g., aerosolized water. For example, liquid waterand steam can be combined at a relative flow ratio (e.g., with flowrates in sccm) 1:1 to 1:10. However, if the amount of liquid water islow, e.g., less than 5 wt %, e.g., less than 3 wt %, e.g., less than 1wt %, then the steam will have superior heat transfer qualities. Thus,in some implementations the steam is dry steam, i.e., is substantiallyfree of water droplets.

The polishing system 20 can also include a cooling system, e.g., an armwith apertures to dispense a coolant fluid onto the polishing pad, ahigh pressure rinsing system, e.g., an arm with nozzles to spray arinsing liquid onto the polishing pad, and a wiper blade or body toevenly distribute the polishing liquid 38 across the polishing pad 30.

Referring to FIG. 2 , the polishing system 20 also includes a controlsystem 200 to control operation of various components, e.g., thetemperature control system 100, as well as rotation of the carrier head,rotation of the platen, pressure applied by chambers in the carrierhead, etc.

The control system 200 can be configured to receive the pad temperaturemeasurements from the temperature sensor 64. The control systemimplements a first control loop 202 that can set a target parameter forthe steam on a cycle-to-cycle basis (each cycle includes a recuperationphase and a dispense phase as discussed above). In brief, the controlloop 202 can compare the measured pad temperature to a target padtemperature, and generate a feedback signal. The feedback signal is usedto calculate a revised target parameter for the steam so as to reach thetarget pad temperature. For example, if the measured pad temperature didnot reach the target pad temperature in a prior dispense phase then thefeedback signal will cause the temperature control system 200 to delivermore heat to the polishing pad in a subsequent dispense phase, whereasif the measured pad temperature exceeded the target pad temperature in aprior dispense phase then the feedback signal will cause the temperaturecontrol system 200 to deliver less heat to the polishing pad in asubsequent dispense phase.

Several techniques can be used, singly or in combination, to control theamount of heat delivered to the polishing pad from dispense phase todispense phase. First, the duration during which the steam is delivered,e.g., the duty cycle, can be increased (to deliver more heat) ordecreased (to deliver less heat). Second, the temperature at which thesteam is delivered can be increased (to deliver more heat) or decreased(to deliver less heat). Third, the pressure at which the steam isdelivered can be increased (to deliver more heat) or decreased (todeliver less heat).

Thus, if the measured pad temperature did not reach the target padtemperature, then the feedback signal can cause the control loop 202 toincrease the target steam temperature, pressure and/or duty cycle forthe subsequent dispense phase. On the other hand, if the measured padtemperature exceeded the target pad temperature in a prior dispensephase, then the feedback signal will cause the control loop 202 todecrease the target steam temperature, pressure and/or duty cycle. As aresult a parameter target value, r(t), e.g., a target value for thepressure or temperature, of the steam can vary on a cycle-to-cyclebasis. In some implementations, rather than operating on acycle-to-cycle basis, the control loop can operate on a continuousbasis, continuously monitoring the temperature of the polishing pad 30and adjusting the parameter target value, r(t), as polishing progresses.

The parameter target value, r(t), is output from the control loop 202 toa proportional integral derivative (PID) controller 204 that performs aproportional integral derivative control algorithm to control the powerapplied by the power supply 250 to the heater 430. The PID controller204 can be connected to the sensor 260 to receive measurements, Y(t), ofthe parameter, e.g., temperature or pressure. The PID controller 204 canbe tuned such that the target parameter value is achieved just beforethe beginning of the next dispense phase. For example, the targetparameter can be reached less than 180 seconds, e.g., less than 60seconds, e.g., less than 30 seconds, e.g., less than 10 seconds, e.g.,less than 3 seconds, e.g., less than 1 second, before the valve isopened.

In the PID controller 204, target parameter value, r(t), is compared tothe measured parameter value, Y(t), from the sensor 260, by a comparator210. The comparator outputs an error signal, e(t), based on thedifference.

The error signal is input to a proportional value calculator 212, whichcalculates a first proportional output P. The proportional output P canbe calculated based on

P=K _(P) e(t)

where K_(P) is a weight set during tuning. The error signal, e(t), isalso input to an integral value calculator 214, which calculates asecond integral output I. The integral output I can be calculated basedon

I=K _(I) ∫e(t)dt

where K_(I) is a weight set during tuning. The error signal, e(t), isalso input to a derivative value calculator 216, which calculates athird derivative output D. The derivative output D can be calculatedbased on

$D = {K_{D}\frac{{de}(t)}{dt}}$

where K_(D) is a weight set during tuning.

The proportional output P, integral output I, and derivative output Dare summed by a sum calculator 218, to output a control signal, u(t),which sets the power output by the power supply 250 to the heater 430.

In general, in tuning the PID controller 204, it is desirable to keepK_(P) as low as possible. 20 Then K_(I) and K_(D) can be increased asnecessary based on overshoot and settling time such that the targetparameter value is achieved just before the beginning of the nextdispense phase. A variety of PID tuning methods are available, such asthe Cohen-Coon method, the Ziegler-Nichols method, the Tyreus-Luybenmethod, and the Autotune Method. In some implementations the amount ofheat applied is controlled under the assumption that the duty cycle ofthe valve is constant. In this case the gain values K_(I), K_(P), andK_(D) need not be varied from cycle to cycle. However, in someimplementations, if the duty cycle changes from cycle to cycle, thenK_(I), K_(P), and K_(D) can be adjusted for each duty cycle. Forexample, the once the duty cycle is calculated, the gain values can beselected based on a look-up-table that associates the gain values K_(I),K_(P), and K_(D) with the duty cycle percentatages.

In some implementations, rather than controlling heat applied by theheater 430, the PID controller 204 can control a flow meter or valve 270that can bleed pressure off the vessel in the steam generator 410. Inthis case, the flow meter or valve is controlled to bleed off pressureto maintain the steam pressure at a target pressure value. Ifimplemented as a valve, the valve can be opened and closed with a dutycycle that depends on the control signal, u(t). If implemented as a flowmeter, the control signal, u(t), can control the flow rate through theregulator, e.g., by adjusting an aperture size. In some implementations,the PID controller 204 can control the valve 438; in this case the steamis discharged through the opening in the arm.

The control system 200, and the functional operations thereof, can beimplemented in digital electronic circuitry, in tangibly-embodiedcomputer software or firmware, in computer hardware, or in combinationsof one or more of them. The computer software can be implemented as oneor more computer programs, i.e., one or more modules of computer programinstructions encoded on a tangible non transitory storage medium forexecution by, or to control the operation of, a processor of a dataprocessing apparatus. The electronic circuitry and data processingapparatus can include a general purpose programmable computer, aprogrammable digital processor, and/or multiple digital processors orcomputers, as well as be special purpose logic circuitry, e.g., an FPGA(field programmable gate array) or an ASIC (application specificintegrated circuit).

For the control system to be “configured to” perform particularoperations or actions means that the system has installed on itsoftware, firmware, hardware, or a combination of them that in operationcause the system to perform the operations or actions. For one or morecomputer programs to be configured to perform particular operations oractions means that the one or more programs include instructions that,when executed by data processing apparatus, cause the apparatus toperform the operations or actions.

Referring to FIG. 3A, steam for the processes described in thisdescription, or for other uses in a chemical mechanical polishingsystem, can be generated using the steam generator 410. An exemplarysteam generator 410 can include a canister 420 that encloses an interiorvolume 425. The walls of the canister 420 can be made of a thermallyinsulating material with a very low level of mineral contaminants, e.g.,quartz. Alternatively, the walls of the canister could be formed ofanother material, e.g., and an interior surface of the canister could becoated with polytetrafluoroethylene (PTFE) or another plastic. In someimplementations, the canister 420 can be 10-20 inches long, and 1-5inches wide.

Referring to FIGS. 3A and 3B, in some embodiments, the interior volume425 of the canister 420 is divided into a lower chamber 422 and an upperchamber 424 by a barrier 426. The barrier 426 can be made of the samematerial as the canister walls, e.g., quartz, stainless steel, aluminum,or a ceramic such as alumina. Quartz may be superior in terms of lowerrisk of contamination. The barrier 426 can substantially prevent theliquid water 440 from entering the upper chamber 424 by blocking waterdroplets splattered by the boiling water. This permits the dry steam toaccumulate in the upper chamber 424.

The barrier 426 includes one or more apertures 428. The apertures 428permit the steam to pass from the lower chamber 422 into the upperchamber 424. The apertures 428—and particularly the apertures 428 nearthe edge of the barrier 426—can allow for condensate on the walls of theupper chamber 424 to drip down into the lower chamber 422 to reduce theliquid content in the upper chamber 426 and permit the liquid to bereheated with the water 440.

The apertures 428 can be located at the edges, e.g., only at the edges,of the barrier 426 where the barrier 426 meets the inner walls of thecanister 420. The apertures 428 can be located near the edges of thebarrier 426, e.g., between the edge of the barrier 426 and the center ofthe barrier 426. This configuration can be advantageous in that thebarrier 426 lacks apertures in the center and thus has reduced risk ofliquid water droplets entering the upper chamber, while still permittingcondensate on the side walls of the upper chamber 424 to flow out of theupper chamber.

However, in some implementations, apertures are also positioned awayfrom the edges, e.g., across the width of the barrier 426, e.g.,uniformly spaced across the area of the barrier 425.

Referring to FIG. 3A, a water inlet 432 can connect a water reservoir434 to the lower chamber 422 of the canister 420. The water inlet 432can be located at or near the bottom of the canister 420 to provide thelower chamber 422 with water 440.

One or more heating elements 430 can surround a portion of the lowerchamber 422 of the canister 420. The heating element 430, for example,can be a heating coil, e.g., a resistive heater, wrapped around theoutside of the canister 420. The heating element can also be provided bya thin film coating on the material of the side walls of the canister;if current is applied then this thin film coating can serve as a heatingelement.

The heating element 430 can also be located within the lower chamber 422of the canister 420. For example, the heating element can be coated witha material that will prevent contaminants, e.g., metal contaminants,from the heating element from migrating into the steam.

The heating element 430 can apply heat to a bottom portion of thecanister 420 up to a minimum water level 443 a. That is, the heatingelement 430 can cover portions of the canister 420 that is below theminimum water level 443 a to prevent overheating, and to reduceunnecessary energy expenditures.

A steam outlet 436 can connect the upper chamber 424 to a steam deliverypassage 438. The steam delivery passage 438 can be located at the top ornear the top of the canister 420, e.g., in the ceiling of the canister420, to allow steam to pass from the canister 420 into the steamdelivery passage 438, and to the various components of the CMPapparatus. The steam delivery passage 438 can be used to funnel steamtowards various areas of the chemical mechanical polishing apparatus,e.g., for steam cleaning and preheating of the carrier head 70,substrate 10, and pad conditioner disk 92.

In some implementations, a filter 470 is coupled to the steam outlet 438configured to reduce contaminants in the steam 446. The filter 470 canbe an ion-exchange filter.

Water 440 can flow from the water reservoir 434 through the water inlet432 and into the lower chamber 422. The water 440 can fill the canister420 at least up to a water level 442 that is above the heating element430 and below the barrier 426. As the water 440 is heated, gas media 446is generated and rises through the apertures 428 of the barrier 426. Theapertures 428 permit steam to rise and simultaneously permitcondensation to fall through, resulting in a gas media 446 in which thewater is steam that is substantially free of liquid (e.g., does not haveliquid water droplets suspended in the steam).

In some implementations, the water level is determined using a waterlevel sensor 460 measuring the water level 442 in a bypass tube 444. Thebypass tube connects the water reservoir 434 to the steam deliverypassage 438 in parallel with the canister 420. The water level sensor460 can indicate where the water level 442 is within the bypass tube444, and accordingly, the canister 420. For example, the water levelsensor 444 and the canister 420 are equally pressured (e.g., bothreceive water from the same water reservoir 434 and both have the samepressure at the top, e.g., both connect to the steam delivery passage438), so the water level 442 is the same between the water level sensorand the canister 420. In some embodiments, the water level 442 in thewater level sensor 444 can otherwise indicate the water level 442 in thecanister 420, e.g., the water level 442 in the water level sensor 444 isscaled to indicate the water level 442 in the canister 420.

In operation, the water level 442 in the canister is above a minimumwater level 443 a and below a maximum water level 443 b. The minimumwater level 443 a is at least above the heating element 430, and themaximum water level 443 b is sufficiently below the steam outlet 436 andthe barrier 426 such that enough space is provided to allow gas media446, e.g., steam, to accumulate near the top of the canister 420 andstill be substantially free of liquid water.

In some implementations, the controller 200 is coupled to a valve 480that controls fluid flow through the water inlet 432, a valve 482 thatcontrols fluid flow through the steam outlet 436, and/or the water levelsensor 460. Using the water level sensor 460, the controller 200 isconfigured to regulate the flow of water 440 going into the canister 420and regulate the flow of gas 446 leaving the canister 420 to maintain awater level 442 that is above the minimum water level 443 a (and abovethe heating element 430), and below the maximum water level 443 b (andbelow the barrier 426, if there is a barrier 426). The controller 200can also be coupled to the power supply 250 for the heating element 430in order to control the amount of heat delivered to the water 440 in thecanister 420.

Although measurements of pad temperature and delivery of steam onto thepad are discussed, this should be understood as including measurementsof the slurry on the pad or delivery of steam onto slurry on the pad.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A computer program product, comprising acomputer-readable medium having instructions to cause one or moreprocessors to: access a polishing process recipe stored as data in anon-transitory storage device; cause a first valve between an outlet ofa steam generation device and an opening to open and close in accordancewith the steam delivery schedule that alternates between a recuperationphase in which the first valve is closed and a dispense phase in whichthe first valve is open; receive from a sensor a measured value for asteam parameter of steam in the steam generation device; receive atarget value for the steam parameter, control a second pressure releasevalve and/or the heating element based on the target value and measuredvalue such that the measured value reaches the target valuesubstantially just before the valve is opened according to the steamdelivery schedule, and open the first valve during a dispense phase of acycle and configured to close the first valve during a recuperationphase of the cycle.
 2. The computer program product of claim 1, whereinthe steam parameter is steam temperature, the measured value is ameasured steam temperature value, and the target value is a target steamtemperature value.
 3. The computer program product of claim 1, whereinthe steam parameter is steam pressure, the measured value is a measuredsteam pressure value, and the target value is a target steam pressurevalue.
 4. The computer program product of claim 1, comprisinginstructions to control the second pressure release valve such that themeasured value reaches the target value substantially just before thevalve is opened.
 5. The computer program product of claim 1, comprisinginstructions to control the heater such that the measured value reachesthe target value substantially just before the valve is opened
 6. Thecomputer program product of claim 1, comprising instructions to controlthe second pressure release valve and/or the heating element based suchthat the measured value reaches the target value less than 10 secondsbefore the first valve is opened.
 7. The computer program product ofclaim 1, comprising instructions to control the second pressure releasevalve and/or the heating element based such that the measured valuereaches the target value less than 3 seconds before the first valve isopened.
 8. The computer program product of claim 1, comprisinginstructions to control the second pressure release valve and/or theheating element based such that the measured value reaches the targetvalue less than 1 seconds before the first valve is opened.
 9. Thecomputer program product of claim 1, comprising instructions to receivea signal from a water level sensor and to modify a flow rate of waterthrough the water inlet based on the signal from the water level sensorto keep a water level in the vessel above the heating element and belowthe outlet.
 10. The computer program product of claim 9, wherein eachcycle corresponds to polishing of a single substrate.
 11. The computerprogram product of claim 9, wherein each cycle consists of a singledispense phase and a single recuperation phase.
 12. The computer programproduct of claim 1, comprising instructions to receive a signalrepresenting the temperature of the polishing pad from a sensor and toset the target value for the steam parameter based on the signal. 13.The computer program product of claim 12, comprising instructions to setthe target value on a cycle-by-cycle basis.
 14. The computer programproduct of claim 12, comprising instructions to set the target value ona continuous basis through a cycle.